Silver halide emulsions sensitized with a combination of sulfur and selenium for color photography

ABSTRACT

CHEMICAL SENSITIZATION OF A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A COLOR-FORMING COUPLER WITH A COMBINATION OF LABILE SULFUR WITH LABILE SELENIUM PROVIDES A SYNERGISTIC INCREASE IN SPEED. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A COLOR-FORMING COUPLER AND SENSITIZED WITH A COMBINATION OF A SULFUR SENSITIZER, SUCH AS SODIUM THIOSULFATE, WITH A SELENIUM SENSITIZER, SUCH AS DIMETHYL SELENOUREA, PROVIDES A SYNERGISTIC INCREASE IN SPEED AND OTHER DESIRED SENSITOMETRIC PROPERTIES.

United States Patent F 3,591,385 SILVER HALIDE EMULSIONS SENSITTZED WlTl-I A COMBINATION OF SULFUR AND SELENIUM FOR COLOR PHOTOGRAPHY Francis J. Evans, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, 'N.Y. No Drawing. Filed Apr. 22, 1969, Ser. No. 818,418

Int. Cl. G03c l/28 U.S. Cl. 96-107 14 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This invention relates to photography. In one aspect this invention relates to chemically sensitizing silver halide emulsions and photographic elements for color photography and to color-recording elements comprising recording layers of such emulsions.

Description of the prior art Photographic color-recording elements typically comprise at least one and usually multiple layers of photographic silver halide, usually a silver chloride or silver chlorobromide emulsion. Each layer is sensitive to a region of the spectrum, e.g., a red-sensitive layer, a greensensitive layer and a blue-sensitive layer, and each can contain a color coupler which forms by color development, as with a p-phenylenediamine or p-aminophenol developing agent, a color image usually complementary to the spectral region to which that layer is sensitive, e.g., cyan, magenta and yellow. Typical color-recording photographic elements and processes of developing an image in such elements are described, for example, in Mees and James, The Theory of the Photographic Process, 3rd edition, 1966, pages 382396. It is known to employ labile sulfur compounds as chemical sensitizers for one or more of the silver halide layers in such a color-recording element. This is described, for example, in US. Pat. 2,956,879 of VanCampen, issued Oct. 18, 1960.

The chemical sensitization of photographic silver halide emulsions containing a color-forming coupler with a combination of a noble metal sensitizer, e.g., a gold compound, and a selenium sensitizer is described, for example, in US. Pat. 3,297,447 of McVeigh, issued I an. 10, 1967 and US. Pat. 3,297,446 of Dunn, issued J an. 1967. Chemical sensitization of these photographic emulsions is not carried out with a sulfur sensitizer or the combination of chemical sensitizers according to the invention.

Moreover, While sulfur sensitizers are known as described, for example, in US. Pat. 1,623,499 of Sheppard et al., issued Apr. 5, 1927, US. Pat. 1,574,944 of Sheppard, issued Mar. 2, 1966 and US. Pat. 2,410,689 of Sheppard et al., issued Nov. 5, 1946, there has been a continuing need for chemical sensitizers which provide 3,59l,385 Patented July 6, 1971 increased detail in high light areas and increased photographic speed of photographic papers for producing color prints. As illustrated in following Example 1, sulfur sensitizers do not provide the desired results that a combination of sensitizers according to the invention provide.

It is accordingly an object of the invention to provide a photographic silver halide emulsion containing an incorporated color-forming coupler and being chemically sensitized with a combination of a sulfur sensitizer with another sensitizer providing a synergistic speed increase without undesired effects on the color-forming coupler and other sensitometric properties.

It is another object of the invention to provide a photographic element containing a color-forming coupler and being chemically sensitized with a combination of a sulfur sensitizer with another sensitizer providing the described properties.

A further object is to provide a method of chemically sensitizing a photographic silver halide emulsion containing a color-forming coupler with a combination of sensitizers as described.

SUMMARY OF THE INVENTION According to the invention, chemical sensitization of a photographic silver halide emulsion, especially an emulsion comprising a photographic silver halide containing at least 10 mole percent chloride with any remainder consisting of bromide and not more than 10 mole percent iodide, containing a color-forming coupler, with a combination of labile sulfur with labile selenium, provides a synergistic increase in speed without adversely affecting the color-forming coupler and development of a color image. Chemical sensitization of a photographic silver halide emulsion containing a color-forming coupler, as described, can be carried outwith a combination of (a) 0.5 mg. to 50 mg. of sulfur sensitizer with (b) 0.05 mg. to 5 mg. of selenium sensitizer per mole of silver present in the emulsion.

A method of chemically sensitizing a photographic silver halide emulsion containing a color-forming coupler comprising Ostwald ripening said emulsion, adding a sulfur sensitizer and selenium sensitizer thereto, and finally digesting the resulting emulsion provides the described synergistic speed increase.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Selenium sensitizers that can be used according to the invention can be selected from a wide group of suitable selenium compounds, such as those described in US. Pat. 1,623,499 of Sheppard et al., issued Apr. 5, 1927, US. Pat. 1,574,944 of Sheppard, issued Mar. 2, 1926, US. Pat. 1,602,592 of Sheppard, issued Oct. 12, 1926 and US. Pat. 3,296,446 of Dunn, issued Jan. 10, 1967. Any selenium sensitizer commonly employed in the photographic art can be employed according to the invention.

Especially useful selenium sensitizers are organic compounds having a selenium atom doubly bonded to a carbon atom by a covalent linkage. These include, for example, selenoamides, selenoketones (especially ketones having an alkyl radical attached to the moiety), selenocarboxylic acids and esters, etc. Preferred selenium sensitizers are aliphatic selenoureas, e.g., alkyl selenoureas having alkyl radicals containing 1 to 8 carbon atoms, e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl radicals. Such selenourea compounds have at least one hydrogen atom on the nitrogen atom available for formation of an enol tautmer. Also useful are aromatic selenoureas having an aromatic radical, e.g., containing 6 to 20 carbon atoms, such as phenyl, tolyl, etc., or a heterocyclic radical such as benzothiazolyl, pyridyl, etc., and aliphatic isoselenocyanates, such as allyl isoselenocyanate. Colloidal selenium is also a suitable selenium sensitizer as are selenophosphones and selenophosphates. Some specific examples of selenium sensitizers useful in the invention are:

N,N-dimethyl selenourea selenoacetone selenoacetophenone tetramethyl selenourea N-(beta-carboxyethyl)-N',N-dimethylselenourea selenoacetamide triphenylphosphine selenide triphenyl selenophosphate allyl isoselenocyanate dioctyleselenourea,

and the like. Selenium compounds which form labile selenium in situ are also suitable, such as described in Belgium Pat. 708,853, issued Feb. 15, 1968, US. Pat. 3,408,- 196 of McVeigh, issued Oct. 28, 1968, US. Pat. 3,408,197 of McVeigh, issued Oct. 28, 1968, and US. application Ser. No. 717,396 of Dunn, filed Mar. 29, 1968, now US. Pat. No. 3,442,653.

A suitable concentration of selenium sensitizer needed for optimum sensitization in accordance with the invention will vary according to several factors, such as the particular selenium sensitizer selected, the nature of the emulsion and time and temperature of digestion and the like. Depending on the particular conditions and other factors described, concentrations of selenium sensitizer can be in the range of about 0.01 mg. to about 20 mg. of selenium sensitizer per mole of silver in the emulsion in accordance -with the invention. In most cases the optimum concentration will fall in the range from about 0.1 mg. to about mg. of the selenium sensitizer per mole of silver.

Sulfur sensitizers useful in combination with the described selenium sensitizers can be selected from any of a variety of useful sulfur compounds known for use as chemical sensitizers, including, for instance, those described in US. Pat. 1,623,499 of Sheppard et al., issued Apr. 5, 1927, US. Pat. 1,574,944 of Sheppard, issued Mar. 2, 1926 and U.S. Pat. 2,410,689 of Sheppard et al., issued Nov. 5, 1946, as well as Mees and James, The Theory of the Photographic Process, 3rd edition, 1966, pages 113-116. Specific examples of useful sulfur sensitizers include:

sodium thiosulfate allyl thiourea thiourea thiosemicarbazide dimethyl thiourea methyl phenyl thiourea,

and the like. Colloidal sulfur is also a suitable sulfur sensitizer.

Concentrations of labile sulfur needed for optimum sensitization according to the invention will vary depending on the several factors described for the optimum concentration of selenium sensitizer, such as the particular sulfur sensitizer selected, the nature of the emulsion, time and temperature of digestion. Depending on the conditions and factors described concentrations of sulfur sensitizer can be about 0.5 mg. to about 50 mg. of sulfur sensitizer per mole of silver in the emulsion. In most cases the range will be about 2.0 mg. to about 20 mg. of sulfur sensitizer per mole of silver in the emulsion.

The ratio of selenium sensitizer to sulfur sensitizer in the described combination can vary depending on the desired contrast of the developed image, the particular selenium sensitizer and sulfur sensitizer, the nature of the emulsion, time and temperature of digestion and the like. For each mole of silver in the emulsion the concentration of selenium sensitizer and concentration of sulfur sensitizer will preferably be within the described ranges.

The term labile has a meaning known in the art of photography and is defined, for example, in US. Pat. 3,408,196 of McVeigh, issued Oct. 29, 1968 and US. Pat. 3,297,446 of Dunn, issued Jan. 10, 1967. It means, for example, with regard to selenium, a material which yields a silver selenide that is insoluble in water at room temperature (20 C.) upon addition to an aqueous silver nitrate solution.

The term non-labile as used herein describing selenium compounds has a meaning known in the photographic art and is defined, for example, in US. Pat. 3,408,- 196 of McVeigh, issued Oct. 29, 1968. It means a material which does not yield a silver selenide that is insoluble in water at room temperature (20 C.) upon addition to an aqueous silver nitrate solution. For example, potassium selenocyanate and selenous acid are non-labile selenium compounds since silver selenide does not precipitate when these compounds are added to an aqueous silver nitrate solution.

One embodiment of the invention is a photographic silver halide emulsion comprising silver halide containing at least 10 mole percent chloride with any remainder consisting of bromide and not more than 10 mole percent iodide, a color-forming coupler and the silver halide emulsion being chemically sensitized with a combination of labile sulfur with labile selenium.

A. wide range of color-forming couplers and processes for forming color images can be employed according to the invention. Suitable color-forming couplers are described, for example, in US. Pat. 3,297,446 of Dunn, ssued Jan. 10, 1967 and US Pat. 3,297,447 of McVeigh, issued Jan. 10, 1967, the disclosures of which are incorporated herein by reference. Suitable color-forming couplers are also described in Mees and James. The Theory of the Photographic Process, 3rd edition, 1966, Chapter 17. The sensitizing addenda and color couplers of the invention can be added to a silver halide emulsion in a variety of ways and at various stages in the preparation of the emulsion. It is preferred to add the sensitizing addenda to an emulsion after completion of the Ostwald ripening and prior to a final digestion. It is preferable to add the sensitizing composition after the silver halide grains have reached substantially their final size and shape. Water-soluble addenda may be added in aqueous solution; other solvents can be used as necessary for more diflicultly soluble sensitizers. Useful organic solvents for this purpose include ethanol, methanol, pyridine, acetone, dioxane and the like; the more polar solvents are preferred. Colloidal sensitizers such as colloidal sulfur or selenium are added as a suspension, such as a suspension in water of other suspending medium. Another method is to first dissolve the sensitizer in a water immiscible liquid, e.g., tricresyl phosphate, dibutyl phosphate, triphenyl phosphate, etc., and then mechanically disperse the immiscible solvent in the emulsion as very small suspended particles carrying the sensitizer. Dispersing agents for color couplers can be employed in the described emulsion, such as set out in US. Pat. 2,322,027 of Ielley and Vittum, issued June 15, 1943 and US. Pat. 2,304,940 of Mannes and Godowsky, issued Dec. 15, 1942.

A silver halide emulsion as described can contain conventional addenda, especially those known to be beneficial in photographic elements, such as gelatin plasticizers, coating aids, antifoggants, such as the azaindines and hardeners such as aldehyde hardeners, e.g., formaldehyde, mucochloric acid, glutaraldehyde bis (sodium bisulfite), maleic dialdehyde, aziridines, dioxane derivatives an oxypolysaccharides.

The described photographic emulsions can be nonspectrally sensitized emulsions, such as X-ray or other nonspectrally sensitized emulsions, or be orthochromatic, panchromatic, infrared and other emulsions. They are typically photographic emulsions containing spectral sensitizers, such as sensitizing dyes as described, for example, in US. Pat. 2,526,632 of Brooker et al., issued Oct. 24, 1950 and US. Pat. 2,503,776 of Sprague, issued Apr. 11, 1950. Spectral sensitizers which can be used include cyanines, merocyanines, styryls and hemicyanines.

Various photographic silver salts can be used in the practice of the invention. These include photographic silver halides, such as silver chloride, silver bromide, silver iodide, as well as mixed halides, such as silver bromoiodide, silver chloroiodide and the like. A preferred photographic silver salt is one which comprises at least mole percent chloride with any remainder being bromide and not more than 10 mole percent iodide. This photographic silver salt has relatively low photographic speed and is typically employed in a photographic paper for producing prints.

The silver halide emulsion layer of a photographic element sensitized according to the invention can contain any of the hydrophilic water-permeable binding materials suitable for this purpose. Suitable materials include gelatin, colloidal albumin, polyvinyl compounds, cellulose derivatives, acrylamide polymers, etc. Mixtures of these binding agents can also be used. The binding agents for the emulsion layer of the photographic element can also contain dispersed polymerized vinyl compounds and include, for example, the rwater-insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.

The silver halide emulsion of a photographic element which can be sensitized according to the invention can be coated on a Wide variety of supports. A reflective white paper support is preferred, such as a baryta coated paper or the like, but the described emulsion can be coated on various reflective supports, such as cellulose nitrate film, cellulose ester film, polyvinyl acetal film, polystyrene film, poly(ethylene terephthalate) film and related films or resinous materials as well as glass, metal and the like. Paper supports such as papers which are coated with alpha-olefin polymers, particularly polymers of alpha-olefins containing two or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylene, butyl copolymers and the like, can also be employed. The reflective support can be tinted with a color hue if desired.

Photographic emulsions sensitized according to the invention can contain speed-increasing compounds, such as quaternary ammonium compounds, polyethylene glycols or thioethers. Useful effects often can be obtained by adding the aforementioned speed-increasing compounds to the photographic developer solutions instead of, or in addition to, the photographic emulsions.

Another embodiment of the invention is in a method of developing a latent image in an exposed photographic silver halide emulsion containing a color-forming coupler with a silver halide developer the improvement comprising employing a photographic silver halide emulsion which is chemically sensitized with a combination of labile sulfur with labile selenium.

Various silver halide developing agents and processing conditions can be employed, typically those employed in the photographic art for developing a color image in a photographic silver halide emulsion containing a colorforming coupler. Suitable developing agents and processing conditions are set out, for example, in U.S. Pat. 2,956,879 of VanCampen, issued Oct. 18, 1960 and in Mees and James, The Theory of the Photographic Process, Chapter 17 (1966).

The following examples are included for a further understanding of the invention.

Example 1.-A red-sensitive silver chlorobromide emulsion (86% bromide) containing a phenolic cyan coupler, 2-(alpha-di-tertiary aminophenoxy-n-butyrylamino)-4,6-dichloro-5-methyl phenol, is divided into portions and the separate portions are chemically sensitized to optimum sensitivity with, respectively, sodium thiosulfate, dimethyl selenourea, and with combinations of the two in the concentrations shown for each portion in Table I. Each portion is coated on white reflective baryta coated paper supports at 35 mg. silver and mg. gelatin per square foot and dried. A sample of each coated portion is exposed through an intensity step wedge to light of daylight quality and then processed by a conventional negative-positive color print process using a phenylenediamine developer followed by stop, fix, bleach and hardener fixing steps. The steps. of the negative color process are described in Example 1 of U8. Pat. 2,956,879 of VanCampen, used Oct. 18, 1960 and are as follows:

The photographic element is processed by immersion in a developer having the following cocposition:

Water-1.0 liter Benzyl alcohol-12.6 cc. Sodium hexametaphosphate (Calgon) 2.0 grams Sodium sulfite, anhydrous-2.1 grams Sodium carbonate monohydrate-26. 8 grams Sodium bicarbonate-29 grams Potassium bromide-0.48 grams Sodium chloride0.7 grams Hydroxylamine sulfate-2.1 grams Color developer (pH at 75 F. 9.96)-4.2 grams 1 -amino N ethyl-N-(beta-methanesulfonamidoethyl)-n1- toluidine sesquisulfate monollydrate.

The resulting element is then immersed in a stop bath for about two minutes. The stop bath has the following composition:

Water-1.0 liter Glacial acetic acid-17.0 cc. Sodium sulfite, anhydrous-20.0 grams The element is then fixed in a both having the following composition:

Water-1. 0 liter Sodium thiosulfate223 grams Sodium bisulfitel2.0 grams Sodium acetate, anhydrous14.0 grams Sodium citrate-17 grams Boric acid-5 .0 grams Potassium alum, granular24.0 grams The element is then washed for 2 minutes in running water at about 73 to 77 F. and then treated in a bleach bath at about 73 to 77 F. for 4 minutes:

Water-1.0 liter Sodium nitrate45 .0 grams Potassium ferricyanide-22.5 grams Potassium bromide-8.2 grams Boric acid-75 grams Borax-0.97 grams The element is then washed for 2 minutes in running water at about 73 to 77 F. and then fixed for 2 minutes in a hardener fixing bath having the following composition:

Water-10 liter Glacial acetic acidlS cc.

Sodium zirconyl sulfate (Zircontan-N)-0.46 gram Sodium bisulfite--17.9 grams Sodium thiosulfate-l67.7 grams Sodium citrate-2.5 grams Boric acid7 .2 grams Potassium alum, granular-45.5 grams Sodium hydroxide, granular-10.4 grams Zinc sulfate monohydrate7.5 grams A negative cyan image is obtained with each sample. Sensitometric data for each emulsion is set out in Table I.

8. A photographic element as in claim wherein said layer comprises silver halide containing at least mole TABLE I Sample Portion N 0. Chemical sensitization cone. in mg./mole Ag.

Relative speed 1 Gamma Dmnx. Dmin.

100 2. 54 2. 1O 0. 12 110 1. 88 2. 08 0. 12 128 2. 56 2. 22 0. 11 145 2. 24 2. 2O 0. l1

1 Measured at 0.30 above fog relative to Sample Portion No. 1.

In positive color print material the reduced gamma and softer toe of a sensitometric curve permits the ad- Vantage of printing more detail in highlight areas. This example demonstrates the synergistic speed increase at optimum sensitization obtained with a mixed sensitize-r of both selenium and sulfur sensitizers. This is apparent in samples 3 and 4 as compared with samples 1 and 2. Also, samples 3 and 4 demonstrate how contrast (gamma) is reduced as the proportion of selenium sensitizer in the mixed sensitizer is increased. This permits selection of a desired gamma within the range of gammas between the extremes by adjusting the ratio of mixed sensitizers.

Example 2.Three color printing papers are made as described in Example 2 of US. Pat. 2,956,879 of Van- Campen, issued Oct. 18, 1960 but using for each of the color recording layers in each element a silver chlorobromide emulsion sensitized with a mixture of sulfur sensitizer and selenium sensitizer as described for samples 3 and 4 of Example 1 above. Results similar to those of Example 1 are obtained upon exposure and processing as set out in Example 1.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. A photographic silver halide emulsion comprising silver halide containing at least 10 mole percent chloride with any remainder consisting of bromide and not more than 10 mole percent iodide, and a color-forming coupler; said silver halide emulsion being chemically sensitized with a combination of labile sulfur with labile selenium.

2. A photographic silver halide emulsion as in claim 1 wherein said emulsion is chemically sensitized with a combination of (a) 0.5 mg. to 50 mg. of a sulfur sensitizer with (b) 0.05 mg. to 5 mg. of a selenium sensitizer per mole of silver in said emulsion.

3. A photographic silver halide emulsion as in claim 2 wherein said sulfur sensitizer is sodium thiosulfate and said selenium sensitizer is dimethyl selenourea.

4. A photographic silver halide emulsion as in claim 1 wherein said labile sulfur is provided by a sensitizing concentration of sodium thiosulfate and said labile selenium is provided by a sensitizing concentration of dimethyl selenourea.

5. A photographic element comprising a support containing at least one layer of a silver halide emulsion comprising silver halide containing at least 10 mole percent chloride with any remainder consisting of bromide and not more than 10 mole percent iodide, and a color-forming coupler; said silver halide emulsion being chemically sensitized with a combination of labile sulfur with labile selenium.

6. A photographic element as in claim 5 wherein said support is a white reflective support.

7. A photographic element as in claim 5 wherein said mixture of labile sulfur and labile selenium are contained in a Water immiscible solvent.

percent chloride with any remainder consisting of bromide and not more than 10 mole percent iodide, said layer being chemically sensitized with a combination of labile sulfur with labile selenium.

9. A photographic element as in claim 5 wherein said labile sulfur is provided by a sensitizing concentration of sodium thiosulfate in said emulsion and said labile selenium is provided by a sensitizing concentration of dimethyl selenourea.

10. In a photographic element comprising a support containing (a) a layer of a photographic silver halide emulsion sensitive to the blue region of the spectrum and containing a color-forming coupler which forms a yellow image upon color development, (b) a layer of a photographic silver halide emulsion sensitive to the green region of the spectrum and containing a color-forming coupler which forms a magenta image upon color development and (c) a layer of a photographic silver halide emulsion sensitive to the red region of the spectrum and containing a color-forming coupler which forms a red image upon color development, the improvement comprising at least one of said layers comprising silver halide containing at least 10 mole percent chloride with any remainder consisting of bromide and not more than 10 mole percent iodide, and at least one of said layers being chemically sensitized with a combination of labile sulfur with labile selenium.

11. A method of chemically sensitizing a photographic silver halide emulsion containing a color forming coupler comprising Ostwald ripening said emulsion, adding a sulfur sensitizer and labile selenium thereto, and finally digesting the resulting emulsion.

12. A method as in claim 11 wherein said photographic emulsion is heated to increase its sensitivity.

13. In a method of developing a latent image in an exposed photographic silver halide emulsion containing a color-forming coupler with a silver halide developer the improvement comprising employing a photographic silver halide emulsion which is chemically sensitized with a combination of labile sulfur with labile selenium.

14. A process as in claim 13 wherein emulsion is chemically sensitized with a combination of sodium thiosulfate with dimethyl selenourea.

References Cited UNITED STATES PATENTS 1,623,499 4/1927 Sheppard et a1. 96107 3,297,446 l/1967 Dunn 96107 3,297,447 1/1967 McVeigh 96107 NORMAN G. TORCHIN, Primary Examiner R. E. FIGHTER, Assistant Examiner US. Cl. X.R. 

